This invention relates generally to oxygen delivery systems, and more particularly to a pneumatically controlled oxygen conserver for providing oxygen on demand (i.e., upon inhalation).
Oxygen delivery systems of the type used by patients with pulmonary emphysema, for example, include a source of oxygen (e.g., an oxygen bottle) for holding a supply of oxygen at pressures of up to about 3000 pounds per square inch gauge (psig), a regulator system for reducing the pressure of the oxygen to a pressure suitable for breathing, and a cannula for delivering oxygen to the patient. To increase the life of the oxygen supply, oxygen conservers are frequently used. These devices interrupt the flow of oxygen to the patient, either in response to exhalation, or at timed intervals, thereby reducing the rate of oxygen consumption.
Conservers are generally of two types, those which operate electronically and those which operate pneumatically. Electronic conservers require a power source (e.g., batteries) for operation, thus necessitating periodic replacement or recharging of the power source. The remaining life of the power source, which patients must take into consideration, can be uncertain. Pneumatic conservers, on the other hand, are operated by the inhalation and exhalation of the patient. They require no power source and thus have a significant advantage over electronic conservers. The pneumatic conserver responds to changes in pressure in the cannula to provide oxygen to the patient during inhalation, and to interrupt the flow of oxygen to the patient during exhalation (when oxygen is not needed). However, typical conventional pneumatic conservers are relatively complex in design, requiring a series of spring-activated diaphragms and the like, to ensure oxygen is promptly delivered when the patient inhales and promptly interrupted when the patient exhales.
Some prior oxygen conservers are selectively operable in two modes, an oxygen conserving mode and a continuous flow mode. In the oxygen conserving mode, oxygen is supplied to the patient on an interrupted basis, as described above. In the continuous flow mode, a continuous stream of oxygen is provided to the patient during both inhalation and exhalation. (Continuous delivery during the entire breathing cycle is not necessary for health reasons, but some patients prefer uninterrupted flow.) Typically, when conventional conservers are switched to the continuous flow mode, they do not continuously deliver oxygen until after the patient inhales for the first time. For patients who prefer continuous flow, this can be disconcerting.
There is a need, therefore, for a pneumatic oxygen conserver which overcomes the disadvantages of prior systems.
Among the several objects of this invention may be noted the provision of a pneumatic oxygen conserver which is selectively operable in either an oxygen conserving mode or in a continuous flow mode, and which is equipped for adjustment of the oxygen flow rate in both modes; the provision of such a conserver which is durable and reliable in operation; the provision of a conserver which quickly delivers oxygen upon inhalation and quickly stops delivery upon exhalation; and the provision of a conserver which begins flow of oxygen prior to inhalation in the continuous flow mode.
Briefly, apparatus of this invention is a pneumatic oxygen conserver for providing oxygen to a patient. The conserver includes a body having a cavity and a main diaphragm dividing the cavity into first and second chambers. A first inlet passage delivers oxygen from an oxygen supply to the first chamber, and a second inlet passage delivers oxygen from the supply to the second chamber. An outlet passage delivers oxygen from the first chamber to the patient. The main diaphragm is movable between a closed position to prevent oxygen flow through the outlet passage and an open position to permit such flow. Vent passaging vents the second chamber. A pressure sensitive valve is connectable to the patient for permitting flow through the vent passaging when the patient inhales and preventing flow through the vent passaging when the patient exhales. Valving along the second inlet passage moves between an open position to permit flow through the second inlet passage to pressurize the second chamber and enable the conserver to operate in an oxygen conserving mode and a closed position to prevent flow through the second inlet passage, vent the second chamber, and enable the conserver to operate in a continuous flow mode. In the oxygen conserving mode, oxygen is delivered to the patient when the patient inhales, and oxygen flow is prevented through the outlet passage when the patient exhales. When the valving is in the continuous flow mode, oxygen is continuously delivered through the outlet passage.
In another aspect of the invention, the conserver comprises, a body, a main diaphragm, a first inlet passage, a second inlet passage and an outlet passage. In addition, the conserver includes a metering orifice positioned along the second inlet passage for restricting flow of oxygen. The conserver also includes a sensing diaphragm extending across a second cavity in the body, dividing the second cavity into third and fourth chambers. A control passage extends through the body connecting the second and third chambers, and a control orifice positioned along the control passage restricts flow of oxygen through the control passage. The sensing diaphragm is movable between a closed position in which flow through the control passage is prevented and an open position in which such flow is permitted. A sensing passage extending through the body to the fourth chamber is adapted for connection to the patient so pressure in the fourth chamber decreases when the patient inhales and increases when the patient exhales. Further, the conserver includes a vent passage extending through the body from the third chamber for venting the third chamber. The sensing diaphragm moves to its open position when pressure in the fourth chamber decreases as the patient inhales to vent the second and third chambers and to move the main diaphragm to its open position to deliver oxygen through the outlet passage to the patient, and the sensing diaphragm moves to its closed position when pressure in the fourth chamber increases as the patient exhales to pressurize the second chamber and to move the main diaphragm to its closed position to prevent flow of oxygen to the patient. The vent passage is sized sufficiently large that the sensing diaphragm moves to its closed position in less than about 500 milliseconds after pressure in the fourth chamber approaches about 22 psig as the patient exhales, and the vent passage is sized sufficiently small that the sensing diaphragm moves to its open position in less than about 500 milliseconds after pressure in the fourth chamber falls below about 21 psig as the patient inhales.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.